Low-Temperature Decoherence of Qubit Coupled to Background Charges

TL;DR

This paper derives an exact formula for the decoherence rate of a Josephson charge qubit interacting with background charges, revealing temperature-dependent behavior and the significant role of impurity states across a broad energy spectrum.

Contribution

It provides an exact analytical expression for qubit decoherence due to background charges, highlighting effects beyond classical approximations.

Findings

Decoherence rate is linear in temperature at low T.

At high T, decoherence rate saturates.

Impurity states over a wide energy range significantly influence decoherence.

Abstract

We have found an exact expression for the decoherence rate of a Josephson charge qubit coupled to fluctuating background charges. At low temperatures $T$ the decoherence rate ${\Gamma}$ is linear in $T$ while at high temperatures it saturates in agreement with a known classical solution which, however, reached at surprisingly high $T$. In contrast to the classical picture, impurity states spread in a wide interval of energies ($\gg T$) may essentially contribute to ${\Gamma}$.